Process for curing tobacco

ABSTRACT

A method is provided for curing tobacco by homogenizing harvested leaves. The leaves may be pretreated in the field to achieve uniform yellowing or they can be yellowed by postharvest conditioning. The leaves are cut into 5/64 inch or smaller size pieces and homogenized in a blending or grinding type machine. The homogenized leaf material is then incubated after which the conditioned leaf material is cured. An important feature of this invention is that the composition of the cured tobacco can be altered and undesirable components reduced or eliminated by regulating the metabolic processes during curing through physical, chemical or biological means.

United States Patent [1 1 Tso et al.

[451 Nov. 5, 1974 1 PROCESS FOR CURING TOBACCO [22] Filed: Jan. 31, 1973[21] Appl. No.: 328,204

Related U.S. Application Data [63] Continuation-in-part of Ser. No.166,963, July 28,

1971, abandoned.

OTHER PUBLICATIONS Leaf Tobacco Composition: The Potentional For GeneticChanges Article in Tobacco by Dr. T. C. Tso,

Vol. 168, No. 17 April 25, 1969 pages 69-73.

The Action of Commercial Cellul-ase Preparations on Alkaloids in TobaccoArticle in Tobacco Science by Dr. Henri Silberman, Vol. 162 No. 12 pages30 32 inc.

Dangerous Properties of Industrial Materials by N. Irving Sax (Text)1969 pub. by Reinhold Book Corp. N.Y. (Third Edition) page 1 126 cited.

Primary Examiner-Melvin D. Rein Attorney, Agent, or Firm-M. HowardSilverstein; Max D. Hensley; William E. Scott 5 7 ABSTRACT A method isprovided for curing tobacco by homogenizing harvested leaves. The leavesmay be pretreated in the field to achieve uniform yellowing or they canbe yellowed by postharvest conditioning. The leaves are cut into 5/64inch or smaller size pieces and homogenized in a blending or grindingtype machine. The homogenized leaf material is then incubated afterwhich the conditioned leaf material is cured. An important feature ofthis invention is that the composition of the cured tobacco can bealtered and undesirable components reduced or eliminated by regulatingthe metabolic processes during curing through physical, chemical orbiological means.

7 Claims, No Drawings PROCESS FOR CURING TOBACCO This application is acontinuation-in-part of our copending application for patent, Ser. No.166,963, filed July 28, 1971, now abandoned.

A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

This invention relates to amethodand procedures for curing harvestedtobacco leaf. More particularly, it relates to the homogenization ofharvested leaf materials and curing the same under special conditions toachieve desired quality and at the same time save the labor in handling.

In usual practice of tobacco production, when tobacco leaves reachmaturity, either the whole plant is harvested by stalk-cutting afterwhich it is air-cured, or each single leaf is primed and flue-cured orair-cured, depending on the tobacco type. In tobacco technology, curingusually refers to changes that harvested fresh leaves undergo whensubjected to regulated conditions of temperature and humidity. It is avital process and falls into the category of starvation phenomena orinanition of excised plant parts. The purpose of curing is to transformthe harvested green material to a form having the physical and chemicalcharacteristics desired for smoking. It is not merely a dehydrationprocess, but involves complicated physical, chemical and biochemicalprocesses.

Conventional curing methods are time consuming and offer littleopportunity for manipulation of the leaf characteristics. Harvest andpost-harvest handling may amount to 50-55 percent of total productiontime. A number of new curing methods have been proposed but none of themattempt to alter leaf composition with a view towards improving tobaccoquality or reducing health-hazard factors. An attempt to develop a newmethod by cutting the tobacco leaves into narrow strips before curingwas found to be unsatisfactory. Reconstituted tobacco sheet, that is, asheet made from finely ground conventionally cured tobacco leaves, whencompared with natural tobacco and standard tobacco blends, producedlower yields of condensate and the condensate exhibited lowertumorigenic activity (To bacco and Tobacco Smoke, Studies inExperimental Carcinogenesis, Ernest L. Wyndler and Dietrich l-loffman,Academic Press, New York and London, 1967, page 79, Tables IV.3 and WAand pages 531 and 532 and FIG. IX.13 (page 531)). In view of thesefacts, it is no longer considered essential to preserve the tobacco leafin its natural fonn during curing and processing.

An object of the present invention is to reduce curing and otherpost-harvest expenses.

Another object is to reduce or eliminate in the tobacco factors that maybe associated with health problems.

A further object is to enhance the desirable properties of tobacco andthus make it more usable.

In general, according to this invention, harvested to bacco i.e.,uncured tobacco, is cured not as the whole leaf but as a homogenizedmass. In addition to being an innovative way of curing tobacco, theinvention is important because the metabolic processes can be regulatedto alter the final composition of the cured tobacco. In addition,undesirable components can be reduced in amount or completely eliminatedby physical, chemical or biological means or combinations of such means.Also, the cured material can be easily stored for aging or otherprocessing such as fermentation prior to being reconstituted formanufacture into a smoking product.

In the practice of this invention, tobacco leaves are removed fromstalks in the field. The tobacco plants may be pretreated in the fieldwith any of the known ethylene-releasing agents to achieve uniformyellowing, or they can be primed, that is, the leaves can be harvestedas they ripen. Leaves from certain varieties may be homogenizedimmediately, while others may need a period of pile conditioning toyellow them before homogenization. The homogenization is carried out ina Waring blender or meat grinder, or similar machine, which cuts theleaf material into five sixty-fourths inch size or less. Depending ontype of tobacco, some liquid may be added during the homogenization,chemicals or enzymes may be added, and the pH of the medium may beadjusted. At this stage the mass is ready for incubation; conditioningand length of time again vary by tobacco type. It is during thehomogenizing and incubating steps that chemical, physical, andbiological means can be used to manipulate and regulate the compositionof the final product. After incubation, the mass is then either spreadinto a sheet form or placed into a container for curing under varioustemperature and moisture conditions as it is dried.

The following examples are illustrative of the invention. It will bereadily apparent from the multiple variables that suitable conditionsmay be found to meet any special requirements desired by the tobaccoindustry or the consumer.

Example 1 Burley tobacco (Burley 21) harvested from a greenhouse wasground in a blender (400 gms. with 200 ml water). The homogenized masswas allowed to incubate in a beaker at room temperature (72-75F) for 24hours and spread onto a support in sheet form at a thickness of 0.5 mm.It was then dried for 16 hours at 72-75F at 40% relative humidity (RH).

Example 2 Burley tobacco (Burley 21) harvested from a green house wasground in a blender without addition of water. The ground material wasdivided into three fractions, A, B and C which were placed in separatecontainers. Nitrogen was bubbled through fraction A and oxygen wasbubbled through fraction B. Fraction C was simply exposed to ambientconditions in an airconditioned room. After 72 hours each fraction wasspread in sheet form as in Example 1. Fraction A was tan colored withblackish overtones; fraction B was reddish tan and more nearly the colorof burley tobacco than fractions A or C; and fraction C was a littledarker than fraction B.

Example 3 Burley tobacco (Burley 21) harvested from a greenhouse wasground in a blender without addition of water. The homogenized materialwas divided into 4 fractions which were incubated for the followingperiods of time: 24, 48, 72, and 168 hours respectively. The fractionswere then spread in sheet form and dried. The

best results were obtained with a 24 hour incubation period.

Example 4 Burley tobacco (Burley 21) harvested from a greenhouse wasground in a blender without addition of water. Fractions were incubated24 hours at 30, 40, and 50 C, respectively. The best results wereobtained at an incubation temperature of 30 C.

Example 5 Example 6 Burley tobacco (Ky. 14) harvested from the field waspassed through a meat grinder and then ground in a blender. Thehomogenized material was divided into two sets of samples. 100 ml ofwater was added to each 200 gm of ground tobacco in the first set ofsamples. 100 ml of 20 percent aqueous ethanol containing 0.03 M sodiummetabisulfite was added to each 200 gm of ground tobacco in the secondset of samples. Samples releasing agent and piled on the floor andcovered with plastic for 12 hours to yellow. Before homogenizing eachgroup was divided into two samples; one sample of each group washomogenized after addition of 10 ml of water to 100 gm tobacco, and thesecond sample after addition of 10 ml of 10 percent aqueous ethanol. Thehomogenates were incubated at 5 and at 25 C for 24 hours with andwithout stirring and were then spread in sheet form and air dried atroom temperature. Treatment of the pale yellow variety sample with 10percent ethanol prior to homogenizing and incubating at 25 C for 24hours with stirring provided the best results. When sprayed withethylene-releasing agents after harvesting, the leaves developed brownspots.

Example 9 aroma while the one containing ascorbic acid was light I brownin color, indicating that the ascorbic acid was not as good a reducingagent as the metabisulfite in respect to the color of the product.Compositional differences between the two treatments are shown in thefollowing table:

Amino "/i Total Sugar Phenol Acid Protein Alkaloid mg/g mg/g mg/g mg/gAscorbic Acid 2.49 27.0 22.80 85.0 2.97 Na Metabisull'ile 3.02 34.523.26 I800 8.7.5

Example 10 from each set were incubated for 0, 12, 24 and 36 hours at30, and 50 C, after which they were spread on a glass plate at athickness of 0.75 mm and then dried either in a forced draft oven (55 C)or at room temperature. No difference in consistency was detectablebetween the two sets of samples. Best results were obtained with anincubation period of 24 hours at 40 C. The homogenate to which the 20percent aqueous ethanol containing sodium metabisulfite had been addedwas much lighter in color than that to which water had been added.

Example 7 Burley tobacco (Ky. 14) harvested from the field was ground,and 100 ml of water was added to each of a number of 200 gm samples ofthe homogenate. K PO was added to some of the samples to adjust the pHfrom 5.4 to 5.8, 6.6 and 7.4, and the samples were incubated 24 hours at40 C, after which they were cast in sheet form and dried at roomtemperature. Best results were obtained at a pH level of 6.6.

Example 8 Flue-type tobacco (pale yellow) was harvested as naturallyripened yellow leaves. Three 200 gm batches of tobacco were homogenizedwith ml of fluid in separate batches. One batch contained 0.002 Mmetabisulfite; the other two contained 7 percent aqueous ethanol. Allsamples were incubated 24 hours prior to spreading into sheets, then airdried for 48 hours at room temperature (25C). One of the samplescontaining ethanol was stirred continuously during incubation; the othersamples were not stirred. Final rapid drying was carried out with hoodexhaust fans. The sample which contained ethanol and had been stirredproduced the best results in color and aroma.

Example 1 l v 6. 7.0 percent aqueous ethanol, not stirred. stirred.

7. 7.0 percent aqueous ethanol containing 0.01 M sodium metabisulfite,stirred.

8. 7.0 percent aqueous ethanol containing 0.01 M sodium metabisulfite,not stirred. The best color and aroma were obtained with conditionnumber 7.

Example 12 Flue-type tobacco (pale yellow) was harvested slightly green.The leaves were stored in a cold room (5C) for one week before using,then one 200 gm batch of leaf material was combined with 100 ml of waterand a second 200 gm batch with 7.0 percent curing, another tohomogenized curing. The results in- Example Burley type tobacco washarvested at maturity and subjected to conventional air curing and tohomogenized curing. The homogenized cured tobacco was lower in nicotine,nitrate nitrogen, ammonia nitrogen, total nitrogen, potassium andcalcium and higher in sugar. There was no significant difference inphenols and phosphorus. Chemical analysis of the cured products is shownin the following table:

Example 14 aqueous ethanol, both solutions containing 0.01 M so- 15 w Mdium metabisulfite. The leaves were then homogen1zed. The batchprocessed in 7.0 percent ethanol had Bottom Leaf Middle whole Plant thebest color and aroma. 1-11.c cc HLC CC HLC CC Chemical analysis of theproducts is shown in the fol- N (7 2 IO 2 73 l 88 3 39 3 O0 3 38 icotme,E lowmg table Nitrate N. 0.85 1.02 0.65 0.98 0.70 0.90 Ammonia N, 0.020.11 0.01 0.16 0.02 0.23 Total N, 3.65 4.08 4.15 4.52 4.35 4.40 AminoSugar.% 2.08 1.12 1.23 1.18 1 50 (11.18 0 Phenols, 0.60 0.57 0.58 0.73.66 .76 ,32 327; Q2); 2? Potassium 5.40 6.15 5.12 5.92 5.02 5.60Calcium, 4.38 5.00 3.45 4.52 3.38 4.28 with water 258 455 2208 1050 500Phosphorus. 0.17 0.18 0.20 0.19 0.22 0.22 With ethanol 2.88 62.5 30.27285.0 6.56

HLC Homogemzed leaf curing. 2CC Conventional curing.

Example 13 m mum-WWW Flue-type tobacco (NC 95), grown in a greenhouseExample 16 1 and yellowed with an ethylene-releasing agent, was MatureBurely tobacco leaf was harvested from a treated with added enzymes. 100g of leaf tissue was greenhouse and rinsed with petroleum ether beforehocombined with 200 ml of water containing 0.01 M mogenization. Thepetroleum ether washings were metabisulfite and homogenized. Thehomogenate was combined and evaporated to dryness. The residue wasdivided into four samples: (a) control, (b) with 0.5 perdiscarded, thepetroleum ether evaporate was collected cent amylase (diastase of malt),(c) with 0.5 percent and returned to the homogenate. After 24hoursincu-- pectinase, and (d) with 0.5 percent protease (bromebation thehomogenate was spread in sheet form and lain). Each sample was stirredvigorously for 20 minair dried. The dried cured sheet showedsatisfactory utes at beginning of incubation period, stirred for 20color and aroma. minutes again 6 hours later and then for 20 minutesExam le 17 again after 18 hours. After 24 hours of incubation time, peach sample was spread out to dry inthe dark under the Mature Burleytype tobacco was harvested from a influence of a moving air currentsupplied by a hood greenhouse and homogenized. Petroleum ether was fan.The control and the amylase and protease treated added to the homogenateto extract petroleum ether dried samples were similar in color, aroma,and texture. soluble components. The petroleum ether fraction was Thepectinase treated sheet was lighter in color, more distilled and thedistillate was retu'med to the homogecompact in texture, and had lesspronounced odor than nate. The residue was discarded. The homogenate wasthe other samples. allowed to stand for 24 hours after which it wasspread Chemical analysis of the products is shown in the folin sheetform and air dried. The cured tobacco showed lowing table: satisfactorycolor and aroma.

Amino Moisture Sugar Phenol Acid Protein retention Z Total (mg/g (mg/g(mg/g (mg/g ("/2 at Alkuloitl sucrose) tyrosme) glycme) BSA) 25C)Control 1.02 56.25 43.42 78.0 15.0 5.0 -Amvlnse 0.77 53.75 32.90 19.210.6 5.6 Peciinase 0.88 36.25 32.94 37.2 7.6 5.0 Protease 0.88 43.7534.02 41.2 8.6 6.6

These results indicate that the chemical composition Example 18 oftobacco material can be modified by addition of en- I Zymcs to thehQmogenatc during the incubation g Leaves were harvested from the lowerhalf of flue type tobacco plants and pile yellowed under plastic sheetsat about 25C. until they were about three quarters yellow. Usually, thispile yellowing process took 2 to 3 days. The leaves on the upper half ofthe plants were yellowed in the field by spraying each plant with aboutml. of an aqueous solution of an ethylene releasing agent,2-chloroethylphosphonic acid (Ethrel). The concentration of the ethrelsolution was such that about 120 mg of the ethylene releasing agent wasdeposited on each plant; that is, about 6 mg/ml. The upper leaves wereharvested about 3 to 4 days after being sprayed. The tobacco leaves werethen homogenized, incubated and dried. During homogenization, dry sodiummetabisulfite was slowly added at a rate of 0.95 g/454 g leaf tissue togive a 0.02 M final concentration to prevent formation of brownpigments. The homogenized material was incubated and dried in a 2.5 cu.ft. mixer lined with Teflon (tetrafluoroethylene fluorocarbon resins)while directing a hot air blast from 300-500F heat gun into the mouth ofthe mixing drum. Additional heat for drying was supplied by means of a250 watt infrared bulb mounted on a common stand with the heat gun.

The homogenized leaf slurry was incubated in batches of to 50 poundswith the mixer rotating at a rate of 25 r.p.m. The combined heat gun andinfrared lamp heated the slurry mass to about 45C. For a 25 lb batch, itrequired 8 hours to remove SOpercent of the moisture. When this state isreached the incubation usually ceases because there is not enoughmoisture present to effect any chemical changes, in the homogenizedtobacco. However, as the moisture level decreases, the rate ofdehydration accelerates so that at the end of 12 hours the moisturecontent is lowered to 4.0 to 5.0 percent which is the final moisturecontent of the homogenized, cured material.

The above described method of continuous agitated incubation and dryingwas found to be far superior to known methods because it preventedexcessive loss of sugars. In conventional static incubation and drying,90 percent of the reducing sugars are lost by oxidation, while in theaccelerated method of this invention 50 to 100 percent of the sugarsordinarily found in barn cured controls were retained. The higheramounts of sugar retention were usually found in the ethrel treatedfield ripened upper leaf material. In addition to the higher sugarcontent, other advantages of the process of this invention are that itprevented loss of those substances that contribute to the aroma oftobacco and it produced a product having a light yellow color.

Example 19 Harvested mature flue type tobacco was homogenized andincubated in the same equipment and under the same condition as inExample 18. Sodium metabisulfite was added at the same rate to give thesame final concentration as in Example 18. After tumbling for. about anhour or less in the mixer, the leaf slurry was dried at about 85C in avacuum oven evacuated to 25 inches Hg. for about 18 hours. This processis even more advantageous than that of Example 18 because the producthas a more pleasant aroma and is even lighter in color than thatobtained in Example 18.

The above results indicate that although accelerated drying is necessaryto prevent loss of sugars, drying under reduced pressure results infurther improvements. The reason for the improvement may be that vacuumdrying prevents enzymatic oxidation of phenolic substances by loweringthe oxygen tension and thereby retarding conversion of phenolic derivedquinones to brown pigments.

Alternatively, the incubated material can be freezedried.

In this process of vacuum or freeze drying, the incubation period forflue-cured tobacco may vary from 1 to 2 hours and that of air curedtobacco from 10 to 24 hours depending on the maturity of the harvestedleaf.

The use of metabisulfite is a common practice in the wine industry. ithas antioxidant properties and as an antiseptic it prevents unwantedfermentation. (The Technology of Wine Making, 2nd Edition, The AVlPublishing Company, Inc., Westport, Connecticut, 1967, M. A. Amerine, H.W. Berg and W. V. Cruess, page 257). The same reference, on page 751,shows that the limit of S0 allowed in wines is 350 p.p.m. Metabisulfiteis used in the process of this invention to control the browningreaction so that the product will not be dark colored. Metabisulfite isinhibitory to the polyphenoloxidase activity which causes browning ofthe homogenized material when the enzyme and substrate come intocontact. It has also been suggested that sulfur compounds may beadvantageous with respect to the smoking and health issues (J. Chromat.57, 239-246, 1971). According to this view, sulfur compounds couldprotect against alkylating agents during the pyrolysis of tobacco.

A comparison was made of the S0 content in tobacco material cured by thehomogenized method with that of conventional barn cured tobacco (varietyCoker 319). The following table shows that only in two out of six caseswas there a notable increase in S0; levels in the leaf, but in no casedid the level exceed the tolerance limit of 350 p.p.m. established forwine.

Although the examples are limited to a few readily available types oftobacco, the process is applicable to many other types. As noted in theexamples, homogenization can be used to modify the chemical compositionof cured tobacco. Further modification can be accomplished by the use ofother techniques during homogenization and incubation such as variabletemperatures, enzyme and microbial action, chemical binding, hydrolysis,removal of undesirable components and addition of desirable components,and aging or fermenting under various conditions. In fact, it is notdifficult to visualize the production of tailor-made tobacco products bythe homogenizedcuring process of this invention.

We claim:

l. A process for curing tobacco comprising the steps of:

a. providing uncured tobacco leaves;

b. homogenizing the leaves in the presence of a 7.0

percent aqueous ethanol solution;

0. incubating the homogenized leaves for-up to about 168 hours at atemperature of from 25C. to C; and

d. drying the incubated homogenate.

2. The process of claim 1 wherein the homogenized leaves are incubatedfor from 18 to 24 hours and are continuously stirred during theincubation period.

3. The process of claim 1 wherein the 7.0 percent aqueous ethanolsolution contains 0.01M sodium metabisulfite and the homogenized leavesare incubated for up to 18 hours.

4. A process for curing naturally and artificially yellowed leaftobacco, comprising the steps of:

a. homogenizing the leaves;

b. adding, during step (a), dry sodium metabisulfite at a rate of 0.95gm. per 454 gms. of leaf tissue to give a final concentration in thehomogenate of about 0.02M metabisulfite;

c. incubating for up to one hour at about 45C. while continuouslytumbling the leaf mass; and

d. drying the incubated homogenate.

5.The process of claim 4 wherein the incubated homogenate is dried by amethod selected from the group consisting of direct application of heat,freeze drying and drying under reduced pressure.

6. A cured tobacco product obtained by the process 10 comprising:

a. providing uncured tobacco leaves;

b. homogenizing the leaves in the presence of a 7.0 percent aqueousethanol solution containing 0.01M sodium metabisulfite;

c. incubating the homogenized leaves for about 18 hours; and

d. drying the incubated homogenate.

7. A cured tobacco product obtained by the process comprising: i I

a. providing naturally and artificially yellowed loaf tobacco;

b. homogenizing the leaves;

c. adding,-during step (b), dry sodium mctabisulfite at a rate of 0.95gms. per 454 gms. of leaf tissue to give a final concentration in thehomogenate of e. drying the incubated homogenate.

UNlTED STATES PATENT OFFICE CETIFICATE OF CORRECTION PATENT NO.3,845,774

DATED" 1 November 5, 1974 |NVENTOR( I Tien C. Tso, Richie H. Lowe andDonald W. DeJong It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

The following statement should appear in the heading in C01. 1:

' Assignee: The United States of America, as

represented by the Secretary of Agriculture.

Signed and Sealed this twenty-second D3) 0f June 1976 '[SEAL] Attest:

RUTH cmsou a c. MARSHALL DANN 4118311718 fficer .(ommissiuner nj'laremsand Trademarks

1. A PRROCESS FOR CURING TOBACCO COMPRISING THE STEPS OF: A. PROVIDINGUNCURED TOBACCO LEAVES; B. HOMOGENIZING THE LEAVES IN THE PRESENCE OF A7.0 PERCENT AQUEOUS ETHANOL SOLUTION; C. INCUBATING THE HOMOGENIZEDLEAVES FOR UP TO ABOUT 168 HOURS AT A TEMPERATURE OF FROM 25*C. TO 80*C;AND D. DRYING THE INCUBATED HOMOGENATE.
 2. The process of claim 1wherein the homogenized leaves are incubated for from 18 to 24 hours andare continuously stirred during the incubation period.
 3. The process ofclaim 1 wherein the 7.0 percent aqueous ethanol solution contAins 0.01Msodium metabisulfite and the homogenized leaves are incubated for up to18 hours.
 4. A process for curing naturally and artificially yellowedleaf tobacco, comprising the steps of: a. homogenizing the leaves; b.adding, during step (a), dry sodium metabisulfite at a rate of 0.95 gm.per 454 gms. of leaf tissue to give a final concentration in thehomogenate of about 0.02M metabisulfite; c. incubating for up to onehour at about 45*C. while continuously tumbling the leaf mass; and d.drying the incubated homogenate.
 5. The process of claim 4 wherein theincubated homogenate is dried by a method selected from the groupconsisting of direct application of heat, freeze drying and drying underreduced pressure.
 6. A cured tobacco product obtained by the processcomprising: a. providing uncured tobacco leaves; b. homogenizing theleaves in the presence of a 7.0 percent aqueous ethanol solutioncontaining 0.01M sodium metabisulfite; c. incubating the homogenizedleaves for about 18 hours; and d. drying the incubated homogenate.
 7. Acured tobacco product obtained by the process comprising: a. providingnaturally and artificially yellowed leaf tobacco; b. homogenizing theleaves; c. adding, during step (b), dry sodium metabisulfite at a rateof 0.95 gms. per 454 gms. of leaf tissue to give a final concentrationin the homogenate of about 0.02M metabisulfite; d. incubating for up toone hour at about 45*C. while continuously tumbling the leaf mass; ande. drying the incubated homogenate.